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1.
2.
Optimization of tool path planning using metaheuristic algorithms such as ant colony systems (ACS) and particle swarm optimization (PSO) provides a feasible approach to reduce geometrical machining errors in 5-axis flank machining of ruled surfaces. The optimal solutions of these algorithms exhibit an unsatisfactory quality in a high-dimensional search space. In this study, various algorithms derived from the electromagnetism-like mechanism (EM) were applied. The test results of representative surfaces showed that all EM-based methods yield more effective optimal solutions than does PSO, despite a longer search time. A new EM-MSS (electromagnetism-like mechanism with move solution screening) algorithm produces the most favorable results by ensuring the continuous improvement of new searches. Incorporating an SPSA (simultaneous perturbation stochastic approximation) technique further improves the search results with effective initial solutions. This work enhances the practical values of tool path planning by providing a satisfactory machining quality. 相似文献
3.
《Journal of Great Lakes research》2020,46(4):899-909
Gmelinoides fasciatus is a successful invasive amphipod (Amphipoda, Crustacea) that dispersed from Lake Baikal to various waterbodies. Here we studied whether Baikal conditions are optimal for G. fasciatus in terms of thermotolerance and investigated lethal temperatures, 70 kDa heat shock protein level, energy metabolism, and antioxidant defense of animals from three geographically distant waterbodies under changing temperatures. We used acute heat exposure to 28 °C to assess the median lethal times and gradual temperature increase from 6 °C to determine the lethal temperatures. Mortality under heat shock was explainable by the baseline content of Hsp70 that correlated with thermal history. But it was not the case under gradual temperature increase where Hsp70 levels became similar and the mortality pattern changed. The most thermotolerant amphipods from the Gulf of Finland demonstrated a higher amount of free glucose during the temperature increase that may be related to the higher salinity of this waterbody and less energy required for ion regulation. Even though concentrations of major physiological ions in Lake Baikal are lower than in Lake Ladoga, G. fasciatus from Ladoga was slightly more sensitive to the gradual temperature increase. This difference could be explained by the influence of high levels of humic and other potentially toxic substances in Lake Ladoga indicated by increased activities of catalase and glutathione S-transferase. Importantly, all G. fasciatus populations accumulated relatively low levels of lactate during the temperature increase, which may reflect the ability of this invasive species to effectively maintain aerobic metabolism under various conditions. 相似文献
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6.
《Energy Policy》2005,33(15):1905-1911
This viewpoint discusses the intra- and international distribution of energy consumption and their implications for intergenerational equity. For global development to be sustainable, the inequality of energy consumption must have an upper limit. A graphic depiction of energy consumption distributions (intra- and international) shows that today's inequalities are large and it is argued that we may have already reached or perhaps even surpassed the sustainability limit of energy consumption inequality. 相似文献
7.
P. C. Campbell E. B. Hawbolt J. K. Brimacombe 《Metallurgical and Materials Transactions A》1991,22(11):2769-2778
The goal of this study was to develop a mathematical model which incorporates heat flow, phase transformation kinetics, and
property-structure-composition relationships to predict the mechanical properties of steel rod being control cooled under
industrial conditions. Thus, the principles of microstructural engineering have been brought to bear on this interdisciplinary
problem by combining computer modeling with laboratory measurements of heat flow, austenite decomposition kinetics, microstructure
and mechanical properties, and industrial trials to determine heat transfer and obtain rod samples under known conditions.
Owing to the length and diversity of the study, it is reported in three parts,[8191]the first of which is concerned with the heat flow measurements. A relatively simple and reliable technique, involving a preheated
steel rod instrumented with a thermocouple secured at its centerline, has been devised to determine the cooling rate in different
regions of the moving bed of rod loops on an operating Stelmor line. The measured thermal response of the rod has been analyzed
by two transient conduction models (lumped and distributed parameter, respectively) to yield overall heat-transfer coefficients
for radiation and convection. The adequacy of the technique has been checked by cooling instrumented rods under well-defined,
air crossflow conditions in the laboratory and comparing measured heat-transfer coefficients to values predicted from well-established
equations. The industrial thermal measurements have permitted the characterization of a coefficient to account for radiative
interaction among adjacent rod loops near the edge and at the center of the bed.
Formerly Graduate Student, The University of British Columbia. 相似文献
8.
A Biologically-Parameterized Feather Model 总被引:1,自引:0,他引:1
Feathers, unlike other cutaneous appendages such as hair, fur, or scales have a definite structure. Variation in feather structure creates a wide range of resulting appearances. Collectively, feather structure determines the appearance of the feather coat, which can largely affect the resulting look of a feathered object (bird). In this paper we define the structure of individual feathers using a parameterization based on biological structure and substructures of actual feathers. We show that our parameterization can generate a large variety of feathers at multiple levels of detail and provide an initial step to semi‐automatically generating a wide range of feather coats. his is achieved by specifying an intuitive interpolation between different structures and ages of feathers. 相似文献
9.
The concept of moving surface boundary-layer control, as applied to a Joukowsky airfoil, is investigated through a planned
experimental programme complemented by numerical studies. The moving surface was provided by rotating cylinders located at
the leading edge and/or trailing edge as well as top surface of the airfoil. Results suggest that the concept is quite promising,
leading to a substantial increase in lift and a delay in stall. Depending on the performance desired, appropriate combinations
of cylinder geometry, location and speed can be selected to obtain favourable results over a wide range of angle of attack.
Next, effectiveness of the concept in reducing drag of bluff bodies such as a two-dimensional flat plate at large angles of
attack, rectangular prisms and three-dimensional models of trucks is assessed through an extensive wind tunnel test-programme.
Results show that injection of momentum through moving surfaces, achieved here by introduction of bearing-mounted, motordriven,
hollow cylinders, can significantly delay separation of the boundary-layer and reduce the pressure drag. The momentum injection
procedure also proved effective in arresting wind-induced vortex resonance and galloping type of instabilities. A flow visualization
study, conducted in a closed-circuit water tunnel using slit lighting and polyvinyl choride tracer particles, adds to the
wind-tunnel and numerical investigations. It shows, rather dramatically, the effectiveness of the moving surface boundary-layer
control (MSBC).
The Sabita Chaudhury Memorial Lecture
The models were fabricated in the Mechanical Engineering Workshop. The assistance of M/s E Abell, P Hurren and D Camp in the
design and construction of the models is gratefully acknowledged. The investigation was supported by the Natural Sciences
and Engineering Research Council of Canada, Grant No. A-2181. 相似文献
10.
On the ontological expressiveness of information systems analysis and design grammars 总被引:9,自引:0,他引:9
Abstract. Information systems analysis and design (ISAD) methodologies provide facilities for describing existing or conceived real-world systems. These facilities are ontologically expressive if they are capable of describing all real-world phenomena completely and clearly. In this paper we formally examine the notion of the ontological expressiveness of a grammar and discuss some of its implications for the design and use of ISAD methodologies. We identify some generic ways in which ontological expressiveness may be undermined in a grammar and some potential consequences of these violations. We also examine ontological expressiveness within the context of some other desirable features that might be considered in the design of ISAD methodologies. 相似文献